It is well known to seal containers or receptacles like glass jars, e.g. for containing (dried and/or powdered) nutritional components such as coffee or spread, with a screwable or clippable plastic cap. In general, the opening of the receptacle is sealably closed by a membrane to hermetically seal the container before the initial opening. Further, a backing layer or support is provided inside the cap to absorb the tolerances between the bottom of the cap and the upper rim of the container. It is thus possible to achieve a certain sealing effect from the ambiance, especially against humidity, when the container is reclosed with the cap after the membrane has been opened/removed from the container. This comes about since the backing layer is pressed against the upper rim of the container.
A heat-sealable sealing element for closing a container having a cap closure is, for instance, known from EP 2 045 194 B1. The heat-sealable sealing element consists of a heat-sealable membrane placed on the whole periphery of the upper rim of the neck of the container or mouth, thereby isolating the container from the exterior, and on the other hand, of a generally thicker support or backing layer, inserted in the bottom of the cap. Prior to the initial opening of the container, particularly before inserting the sealing element in the cap, the support and the heat-sealable membrane are joined by means of a temporary adhesive. The relatively thick and stiff heat-sealable membrane is opened by the consumer not by punching or tearing, but rather by peeling it off from the upper rim of the container using a tab.
In practice, the sealing element is inserted at the bottom of the cap and retained therein via a retention bead of the cap. Once the container is filled, the cap provided with the sealing element is screwed or clipped to the container. The heat-sealable membrane of the sealing element is then in contact with the mouth. The heat-sealable membrane is then sealed to the mouth by induction heat-sealing. Upon opening the container for the first time, the support inserted at the bottom of the plug is detached from the heat-sealable membrane which remains sealed on the upper rim of the container. A temporary adhesive provided between the heat-sealable membrane and the support will be broken preferably by shearing as a result of the separation of the heat-sealable membrane sealed on the container and the support retained in the cap via the retention bead. As the heat-sealable membrane is made from a stiff material a relatively great opening torque (particularly when the cap is screwed to the container) or opening force (particularly when the cap is clipped to the container) is required when the user opens the container for the first time. This great opening torque or force is caused by the fact that at the time of the initial opening the relatively thick heat-sealable membrane has to pass the retention bead. Further, there is a risk that the heat-sealable membrane and support (or backing layer) stick together during an opening of the receptacle due to the temporary adhesive between the heat-sealable membrane and the support such that either the heat-sealable membrane is lifted from the receptacle thus exposing the product to the ambiance or the support is pulled out of the cap by passing the retention bead.